Bacteria rapidly develop resistance to antibiotic drugs within years of first clinical use. Antibiotic resistance can be acquired by horizontal gene transfer or result from persistence, in which a small fraction of cells in a population exhibits a non-inherited tolerance to antimicrobials. Antimicrobial drug discovery is increasingly lagging behind the evolution of antibiotic resistance.
Bacterial infections are responsible for significant morbidity and mortality in clinical settings. Though the advent of antibiotics has reduced the impact of bacterial diseases on human health, the constant evolution of antibiotic resistance poses a serious challenge to the usefulness of today's antibiotic drugs. Infections that would have been easily cured by antibiotics in the past are now able to survive to a greater extent, resulting in sicker patients and longer hospitalizations. The economic impact of antibiotic-resistant infections is estimated to be between US $5 billion and US $24 billion per year in the United States alone. Resistance to antibiotic drugs develops and spreads rapidly, often within a few years of first clinical use.